Summary of Work: AIMS: As many as 50% of AIDS patients suffer from multiple neurological symptoms collectively termed as AIDS-related dementia. The neurotoxicity of the HIV-1 envelope protein gp120 has been implicated in the neuropathology of AIDS. Results from several laboratories indicate that gp120 causes the death of neurons both in vivo and in vitro. While multidisciplinary studies have been conducted on the neurotoxic effects of gp120, the mechanisms responsible for these effects are not well understood. Since it was suggested that activation of microglia by gp120 may be responsible for the HIV-1 induced neurotoxicity, the main purpose of this project was to examine the mechanisms of gp120-induced neuronal cell death in rodent mixed neuron/glia cultures. ACCOMPLISHMENTS: Although the neurotoxicity induced by the HIV-1 envelope protein, gp120, has been demonstrated to require the presence of glial cells (microglia/astrocytes), the mechanisms for the gp120-induced neurotoxicity are not well understood. Moreover, the neurotoxic potencies of gp120s obtained from various HIV isolates are different. Since nitric oxide (NO) and proinflammatory cytokines (TNF-a, IL-1, IL-6) produced by glial cells have been involved in the neuropathogenesis of various diseases, this study examined the effects of gp120 obtained from two strains, HIV-1IIIB and HIV-1SF2, of the HIV-1 virus on the production of NO, and proinflammatory cytokines in murine primary mixed glial cell cultures. The glial cells exposed to HIV-1IIIB gp120 released NO, TNF-a, and IL-6 in a dose dependent manner, whereas IL-1a and IL-1b were undetectable. The cells exposed to HIV-1SF2 gp120 increased the release of IL-6 only. The neurotoxic potencies of these two strains of HIV-1 were well-correlated with their effects on cytokine release. To investigate the cellular sources and mechanisms of the gp120-induced IL-6 production, in situ hybridization with the mRNA for IL-6 was performed in HIV-1IIIB gp120- or HIV-1SF2 gp120-stimulated microglia-enriched or astrocyte-enriched cultures. HIV-1IIIB gp120 or HIV-1SF2 gp120 induced the expression of IL-6 mRNA in both microglia-enriched and astrocyte-enriched cultures, indicating that both microglia and astrocytes produce IL-6, and that the transcriptional regulation is involved in the gp120-induced IL-6 production. Taken together, these results demonstrate that the production of NO, TNF-a, IL-1, or IL-6 from glial cells is differentially regulated by HIV-1IIIB gp120 and HIV-1SF2 gp120. These results may provide insight into the roles of NO and proinflammatory cytokines in the neurotoxicity of gp120s and the neuropathology of different strains of HIV-1 viruses.